Topic: Roland R-07 32-bit floating point!

[TheJez]

(1) Are the R-07 preamps as good as the Zoom F3's? Your idea is all about optimising gain staging with the R-07, but your results will still be worse if the F3 provides cleaner gain. You could use a cleaner external pre-amp like most of us have done in the past, but then you add to bulk.

Obviously the F3 preamps are substantially better. And no matter what processing you do after the ADC's: It will not improve the preamps. However, what I think the software program would do is 'helping getting the best out of your R07'. Until now the 'safety track' has been considered merely as a backup in case you set the levels too high (probably helped by the name that was put on this track by the Roland marketing department). My idea is to consider it as 'just a 2nd ADC' like is implemented on the 32bit recorders like the F3. Let the main track clip and unlock/profit from the extra 20dB headroom that's in your R07! It allows you to set the level higher and therefor beat the noise (I hope)! 

(2) How much work would it take to write a piece of software that accomplished what you're proposing automatically? Because doing it all manually would be a huge pain - not worth it at all unless you absolutely had to. If you are willing to actually write the software, though, it's a good idea!

It doesn't seem like rocket science and the heavy work of reading/writing audio files can be outsourced to available libraries like libsndfile. It depends a bit on how fancy and fool-proof it has to be, and if it should run on Linux/Windows/Mac, command line or graphical user interface etc, but I think a couple of hours work would be enough to get a working prototype... It would be fun to make, I just started a bit already.
The availability of real world example input files would be very helpful for testing! The recording described by Roffels seems like the perfect example: High dynamics and a clipping main track.

@Roffels: Do you still happen to have the main and safety track of the recording you described? And if so, would you be willing to share these with me for testing? That would be awesome!

EDIT: Roffels replied that he unfortunatly doesn't have these tracks anymore. So if there is any other R07 owner that has or can create a clipping main track and the accompanying safety track, please let me know. Even a clipping recording by your R07 in 2xWAV mode of your home stereo set would be sufficient!

[Niels]

The Roland R-07 deck allegedly has an "innovative Hybrid Limiter" function which is supposed to automatically combine a higher and lower level recording.

"Hybrid Limiter" is mentioned in most of their marketing material, but there is no official documentation as to what exactly it does and how it does it - at least not that I have encountered.

There is no mention of Hybrid Limiter in the owners manual. The quoted Roland FAQ below refer to more information in the Reference Guide p. 16, but that does not mention anything about the Hybrid Limiter.

A MusicRadar.com review states the following:

Though the R-07 is a stereo recorder, you can set it to create a WAV and MP3 file simultaneously (Wave+MP3 mode), or use 2xWAV mode to record a second WAV file padded down by 20 dB. If there’s any clipping in the louder file, you can edit between them or, using Hybrid Limiting mode, have the R-07 switch between them automatically.

The R-07 online FAQ tells us when it operates, but not what it does:

The Hybrid Limiter function on the R-07 operates under the following conditions.

"Limiter": ON
"Input Level": 60 or higher

* The Hybrid Limiter function does not operate when Rec Mode is set to "2xWAV (Dual Level Recording)."
* When the Limiter is ON and the Input Level is 59 or lower, or whenever the Dual Level Recording is being engaged, the normal (non-Hybrid) limiter will be activated.
* For more details about the Limiter function and its settings, refer to the Reference Guide (p. 16), "Using Limiter or AGC."

I have not tried it out to see how it performs. I was curious about the function when I got my R-07, but when I learned from the FAQ that it is only active when input level was set to 60 or more, it became irrelevant as my deck is always set lower when recording music.

[Gutbucket]

I'm back in town after a month away and just came across this thread.  Interesting stuff.

@TheJez-
My take on all this that you are spot on.  You describe accurately how the new "32-bit recorders" operate, which might be more accurately described as those which "automatically switch between multiple ADCs" regardless of what output format they are instructed to write (32bit in most but not all cases). The most significant operational difference with the R-07 is that it simply stores the two resulting files that were recorded through parallel signal paths with different gain settings and does not do the "automatic switching" and combining part.  As you speculate, the automatic switching and choice of file output format could be done afterward on the computer as a post-processing step.  Would of course need the appropriate software routine to do that automatically to a similar standard of quality as achieved in the "32bit recorders".  The "magic" of the process is probably routed in the details of the switching comparator routine.

As I understand it. Zoom and Deity "32 bit recorders" auto-switch between two ADCs, so the scheme you describe using the two output files from the R-07 would be most similar to their approach.  SoundDevices apparently switches between 3 separate ADCs.  Same idea, different implementation particulars.

Note- Some folks mentioned the noise floor of the 'safety track'.. there will also a more elevated noise floor in one or two of the multiple ADC paths through any "32 bit recorder".  We just don't notice it because the switching between those paths is done automatically.  When the SPL is low the channel with a higher noise floor is not in use, when SPL is high it masks the noise.


@Niels-
I also was unable to find any additional information on the "hybrid limiter" function of the R-07.  Although it refers to p16 of the Reference Guide for more details, neither that page no any other in the reference guide, user manual, or system update summary has any mention of the "hybrid limiter" or its method of operation.

However, this gives us some hint-

* The Hybrid Limiter function does not operate when Rec Mode is set to "2xWAV (Dual Level Recording)."

That makes it sound like it might be using both parallel signal paths (when they are not already being employed by Dual Level Recording), and automatically switching between them as required.  That is indeed quite similar to what the "32bit recorders" that automatically switch between multiple ADCs are doing.  It may represent an early version of something very similar.  I suspect the difference is in the sophistication of the automatic switching comparator. 

20 years ago I schemed about a method of recording automatic markers that noted when gain was manually adjusted during a recording and by how much.  That information could then be used afterward to automatically find and "undo" those manual gain changes as a post process in the DAW.  Additionally, that functionality could be combined with ACG to provide an end result similar to what the 32bit float recorders are doing today.  Rather than using multiple signal paths through the recorder and combining them in real time or afterwards as a post process, it would instead mark and record all the automatic gain changes, so as to undo them later.  Requires immensely less data storage that way as the only thing additional being stored is the marker positions and gain values.  Conceptually similar to what a compander does, or at a more fundamental and abstract level, how the representation of SACD data values works.

[Niels]

@gutbucket
Sounds plausible.
I have been mildly curious about this Hybrid Limiter since I bought my R-07.
If I didn’t already have plans of getting a Tascam FR-AV2, I’d probably be more motivated to explore what Hybrid Limiter does in practical use.

[adrianb]

Some interesting theories here.

I will have to do some testing with my R07. It’s still my goto device for stealth recording, with 3.1v of PIP I have always found it okay with my CA mics without a battery box. With the Bluetooth and safety track it’s the ultimate stealth recorder imho.

Following the discussion here I need to test this device with the limiter enabled rather than the safety track. Maybe it will make upgrading to a small 32-bit recorder unnecessary. I already have that in my Mixpre-3 if needed.

I’ve only had to use the safety track once, and because it was a louder than expected show (obviously) I didn’t notice any noise. I will have to check back to see if I still have the files for TheJez.

[TheJez]

I’ve only had to use the safety track once, and because it was a louder than expected show (obviously) I didn’t notice any noise. I will have to check back to see if I still have the files for TheJez.

That would be great, thanks! In fact I would already be very happy if you maybe could record in 2xWAV mode your home stereo playing some music for a couple of minutes, and the recording level set so high it will clip the main track considerably. Internal mics would be fine... 

[Gutbucket]

@gutbucket
Sounds plausible.
I have been mildly curious about this Hybrid Limiter since I bought my R-07.
If I didn’t already have plans of getting a Tascam FR-AV2, I’d probably be more motivated to explore what Hybrid Limiter does in practical use.

The term "hybrid" is pretty vague and can mean different things.  FYI, the Zoom F8 [original version, not sure about the later N, and current N-Pro (32bit) version] includes options for standard limiter and "Hybrid Limiter", and also has a safety track option, which when engaged cuts total channel count by half as expected.  In the F8's case the hybrid limiter doesn't switch between primary and safety tracks, but rather implements a scheme using a variable compression ratio and look ahead.  Rather than setting an activation threshold above which the limiter is engaged, the user instead sets a "not to exceed" level and a pad is engaged to increase available headroom. As the signal approaches the set value the limiter starts to engage about 10db lower than the target value and ratio increases as the signal approaches the target value.

Although I prefer setting levels and not using limiters, the output of my mics can sometimes clip the mic-level inputs of the F8 when recoding on stage near the drum kit.  For that reason I started employing its Hybrid Limiter option.  I was surprised to find it very transparent sounding with no obvious limiting artifacts, and also found that the pad did not cause an audible increase in the noise-floor, so I now leave it on all the time and either set levels to target peaking just below the presumed activation threshold, or turn gain all the way down for  high SPL dynamic situations and just let it do its thing to keep peaks from exceeding 0dbFS.

I could leave the gain all the way down and just run it like that for all amplified shows - essentially the same way one runs a 32-bit recorder.  I really only adjust gain out of habit, to achieve a good nominal starting level for editing, and as a back-door way to manage Mid/Side ratio, due to a playback quirk of the F8 not allowing ratio adjustment during playback.  Not sure if I could do the same for classical material where the ambient noise-floor is considerably lower, but I generally use a different rig for that anyway.

I relate all this here because it is effectively yet another way of running without having to adjust gain. 


Edit- I just realized Zoom actually terms the above limiter option "Advanced Limiter" rather than "Hybrid Limiter".. so, different name than Roland's, however it's mode of operation and how I use the recorder is really what I wanted to share.

[TheJez]

@gutbucket
Sounds plausible.

Plausible indeed. However, if the the R07 is going to use both signal paths with this 'hybrid limitter' to combine it to a single 24 bit output, it has to lower the amplitude of the main track by 20dB to make some headroom to add data from the 'safety track path'. As we can't go above 0dbFS with 24 bit. Or something like that... The fact that this feature is so poorly documented and hardly marketed kind of hints that the quality of the used algoithms may be under par...
It seems Roland was on the right track towards multi-ADC recording, so a pitty they didn't push forward with this (yet).

[adrianb]

Just been testing my R07 at home and think I can hear evidence for some of the theories mentioned here.

I always have my R07 set at 2xWAV-24bit with the safety track set at -12dB. The limiter is set to ON.

With my input level set at 60 I recorded some music from my hi-fi with the volume turned up to achieve clipping. I then recorded the same music at the same volume, but with the safety track turned off. The R07 displays the clipping lights in both instances.

On listening back to the files I can hear the limiter kicking in on the first recording, but on the second recording, the one with no safety track it sounds flawless.

It could be placebo effect, but I don’t think so. Could this be the mythical “hybrid limiter” at work?

[TheJez]

This hybrid limiter is interesting indeed, but would you dare to use it on a recording, knowing you'd be just fine using the tried 2xWAV method?
Anyway, back to the original subject: Trying to auto-merge the main and safety tracks of a 2xWAV recording...
Thanks to Adrian I now have an R-07 recording consisting of a clipping main track and the safety track that I can use to analyze and test my program.
It turns out that my initial ideas were a bit naive. The clipping behaves more complicated than I expected, as already hinted in the SD patent description. It seems that very slight clipping makes a single or a few samples reach the max/min value of 24bit samples, and that's it. These seem rather easy to recover from the safety track. However, more severe clipping results in a rather long period (e.g. ~120ms) of mutilated samples. The simple idea 'replace samples > clipping threshold with an amplified sample from the safety track' will not work here. This requires far more intelligent signal processing to accurately 'detect & patch' those periods.
Also I'm having troubles to accurately enough detect the gain difference between left/right main & safety channels and to find out what the DC component is, and what the variation of gain and DC is for each channel. (I know, a varying DC component seems weird by definition, but not unrealistic due to temperature variations...)
The attached picture shows a part of such a 'major clipping' episode. Notice the chopped-off tops of the waves, which are not flat and are not on 0dB. I guess in these cases the pre-amp or the analog part of the ADC was overloaded and need some time to recover.
I'm affraid making a good enough merger requires skills and time beyond what I can offer. It has been fun to work on this and I learned a lot about 32bit float, dual ADC etc. and ended up buying the nice new Tascam FR-AV2 

[capnhook]

Good explanation of the problem, tjanks



Practically, I would simply lower the .wav 2dB

Run RX8 declip

Normalize back to 0dB and call it done



You sweat too much..

[Gutbucket]

 @TheJez-  Thanks for your exploration into the particulars of what it would take to make it work as a post-production process in a practical sense.

Just been testing my R07 at home and think I can hear evidence for some of the theories mentioned here.

I always have my R07 set at 2xWAV-24bit with the safety track set at -12dB. The limiter is set to ON.

With my input level set at 60 I recorded some music from my hi-fi with the volume turned up to achieve clipping. I then recorded the same music at the same volume, but with the safety track turned off. The R07 displays the clipping lights in both instances.

On listening back to the files I can hear the limiter kicking in on the first recording, but on the second recording, the one with no safety track it sounds flawless.

It could be placebo effect, but I don’t think so. Could this be the mythical “hybrid limiter” at work?

Seems that's the case.  And seems to indicate the "hybrid limiter" does a better job than running a safety track, as it similarly accommodated the clipping yet without any perceivable limiting, and without the extra stored tracks to deal with or any additional work.  That makes running the R-07 in that way as your regular mode of operation attractive.

At the very least, that test seems to indicate a good reason not to engage the standard limiter AND the safety track at the same time.  If recording the safety track, I see no reason to also get limiting effects that use of the safety track will avoid along with outright clipping.  Just remains to be seen if the hybrid limiter alone serves to cleanly accommodate more severe clipping that a safety track WIHTOUT the standard limiter engaged might be able to handle.

[adrianb]

Seems that's the case.  And seems to indicate the "hybrid limiter" does a better job than running a safety track, as it similarly accommodated the clipping yet without any perceivable limiting, and without the extra stored tracks to deal with or any additional work.  That makes running the R-07 in that way as your regular mode of operation attractive.

At the very least, that test seems to indicate a good reason not to engage the standard limiter AND the safety track at the same time.  If recording the safety track, I see no reason to also get limiting effects that use of the safety track will avoid along with outright clipping.  Just remains to be seen if the hybrid limiter alone serves to cleanly accommodate more severe clipping that a safety track WIHTOUT the standard limiter engaged might be able to handle.

I have a gig on Saturday. I wasn’t going to record it but will now use it as an chance to experiment. I’m going to go in with my R07, no safety track and input level slightly higher than usual, and see what happens.

[adrianb]

Just got back from the gig I mentioned above. DPA4061s > Battery Box> R07.

It was a loud gig, and I was close to the front.

I normally set the input level at 50 and use a -12dB safety track. Only once have I had to use the safety track.

On this occasion I set the input level at 60 to deliberately force clipping. First half of the show I employed the -12dB safety track with limiter, second half I disabled the safety track.

The main track in the first half exhibits signs of clipping, but I have to say the limiter does quite a good job, better than my M10,  and the recording is very listenable. The safety track is the one I would work with though.

The second half recording is quite extraordinary though, flawless in fact. The limiter is definitely doing a better job when the safety track is not employed.

In future I think I will set the input level at 55 and disable the safety track. I’m buying the Tascam FR-AV2 but think the R07 is still the best stealth recorder.

[AbbyTaper]

No downside in keeping the safety track active is there?  I would think just for peace of mind, if anything.